1. Field of the Invention
The invention relates to a method for purifying a gas stream loaded with organic gases or vapors especially to near the saturation limit in a sorption filter, as well as to an arrangement for carrying out this method.
2. Description of the Prior Art
In gas-purifying technology, vaporous organic substances are separated in many cases from the gas stream to be purified by adsorption in a sorption medium, preferably activated carbon. For this purpose, the gas stream is conducted through a layer of granular sorption medium and during its travel through the layer turbulence and diffusion transport the molecules to be separated into the activated carbon, where they are retained by adsorption and capillary condensation. In the process, adsorption heat is released, which heats up the sorption medium and the gas stream to be purified. This temperature rise which is substantially determined only by the concentration, reaches such values at high concentrations of the substances to be separated that the separation is impeded thereby because the attainable equilibrium loadings drop with increasing temperature. Thereby, the concentrations of organic impurities in the gas subjected to purification in the sorption medium remain relatively high. In addition, the danger of ignition or more generally, the danger of undesired chemical reactions is increased by the temperature rise. In order to decrease the temperature rise, an amount of atmospheric air is frequently admixed to the gas stream to be purified to reduce the concentration of the substances to be separated to desirable low values before entering the sorption medium bed. However, with the increase of the gas stream to be purified, the power requirements of the blowers and in many cases also the size of the sorption filters increase. In particular, however, the product of the emission from the sorption filter has a concentration and a gas flow which remains high even though the concentration is lowered by addition of air, because the gas stream is increased at the same time.
German Published Non-Prosecuted Application No. DE-OS No. 30 20 656 attempts to avoid these disadvantages by two measures: Instead of one activated-carbon bed, several are connected in series, and the gas stream to be purified is always conducted over a cooler between two beds and thereby cooled. Through these intermediate cooling operations, it is possible to remove the adsorption heat. A still present high concentration of organic substances in the gas can be eliminated by post-combustion according to the proposal of DE-OS No. 30 20 656. In order to obtain, according to this proposal, the desired or required low emission values, an elaborate structure of the sorption filter with intermediate coolers inserted between a multiplicity of sorption medium stages and optionally, additional post-combustion may be necessary. Thus, not only must the equipment expense be taken into account but the power consumption for the intermediate cooling and maintenance of the post-combustion must also be taken into consideration.